In connection with so-called jump-lifts, the elevator hoistway is taken into use already before the full length of the elevator hoistway has been completed. The top part of the elevator hoistway is constructed at the same time as an elevator car moving in the already completed bottom part of the elevator hoistway serves people on the lower floors of the building. In jump-lifts, the elevator car moving in the lower part of the elevator hoistway is supported and moved during the construction-time use suspended on hoisting ropes that are supported by a supporting platform in the elevator hoistway, which ropes are moved with a hoisting machine that is usually supported on the supporting platform. The installation work in the upper parts of the elevator hoistway above this supporting platform is done from a movable platform or corresponding. When the part of the elevator hoistway under construction above the supporting platform has reached a sufficient stage of completion, the completed part of the elevator hoistway can be taken into use. In this case a jump-lift is performed, wherein the supporting platform is raised to a higher position in the elevator hoistway, thus extending the operating area of the elevator car upwards. A worksite crane in use in the construction of the building or a lighter hoisting appliance to be supported on the building and arranged for the site for the purpose of the elevator installation can, for example, be used for the lifting. When the elevator hoistway has reached its final height, the supporting platform has conventionally been removed from the elevator hoistway and a machine room has been built at the end of the elevator hoistway, after which the final hoisting machine of the elevator has been brought to the machine room. In prior art the support structure of the supporting platform is formed by keeping the number of support elements small and by arranging the supporting platform to be supported by only two walls of the elevator hoistway that are opposite each other. A problem has been that it has not been possible to utilize the same support structure solution sufficiently freely in elevator solutions that are different types in terms of their layout. The supporting process of the supporting platform has also caused problems. Supporting has earlier been slow to perform, the structures used for supporting have been complex, and the structure achieved has been awkward to make stable without excessively impacting the compactness of the elevator or the other elevator components. Arranging advantageous support for the supporting platform, particularly in the final phase of the process, has been a problem. It has also been a problem that, in order to stabilize the supporting, the placement of components supported by the supporting platform has been awkward to arrange while keeping the structure stable. Additionally, improving the safety of personnel is a continuous objective. In addition, further utilization of the structures has not been sufficient.